Nowadays, various communication protocols are used to establish standard rules for data representation, signaling, authentication and error detection required to send information over communication channels. One of the communication protocols widely used today is the High-Speed Downlink Block Access (HSDPA) which is a technology upgrade to current Universal Mobile Telecommunications System (UMTS) networks.
High Speed Downlink Packet Access (HSDPA) is a packet based data service feature in WCDMA standard providing high speed downlink transmission and belonging in the High-Speed Packet Access (HSPA) family.
Specifically, HSDPA uses four channels for achieving downlink transmission. High-Speed Downlink Shared Channel (HS-DSCH) is a first channel (which is a transport channel) used to send blocks on the downlink to the User Equipments (UEs). High Speed-Shared Control Channel (HS-SCCH) informs the user that data will be sent on the HS-DSCH. Uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH) is a third channel used to carry acknowledgment (ACK)/negative acknowledgement (NACK) information and current Channel Quality Indicator (CQI) of the UE. Finally, High Speed-Physical Downlink Shared Channel (HS-PDSCH) is a fourth channel used by the HSDPA and is added to UMTS in order to increase downlink data rate. It carries information from the HS-DSCH transport channel.
In HSDPA, the downlink data rate is determined by and is under the control of the NodeB which, parallely to the UE, performs its own calculation of the Channel Quality Indicator (CQI) corresponding to an Adaptive Modulation and Coding (AMC) determining the characteristics of the transmission. AMC consists in the three following parameters: a) number of High Speed-Physical Downlink Shared Channel (HS-PDSCH) codes, b) modulation and c) transport block size.
FIG. 7 shows an illustrative example of the CQI mapping table for UE category 10 and which is also described in GPP 25.214 (table 7D in the original document). It can be seen that an increasing transport block size corresponds to an increasing CQI value. Different CQI mapping tables exist for different UE categories.
Generally speaking, in order to achieve a sufficient compromise between a high data rate in the downlink link and a sufficient quality of data communication, the characteristics of the data transmission in the downlink are controlled by the NodeB so as to correspond to a Block Error Rate (BLER) equal to 10%, in accordance with the requirements defined by 3rd Generation Partnership Project (3GPP).
A Block Error Rate (BLER) of 10% on the HS-PDSCH corresponds to the number of negatively acknowledged blocks reported by the UE to the NodeB.
For inducing a BLER of 10%, NodeB selects a CQI (with the help of the CQI reported by the UE) that provides this BLER value and transmits to the UE an AMC corresponding to the selected CQI. For example, in 3GPP 25.214 table 7B, shown in FIG. 3, the NodeB may select a CQI value varying between 0 and 30 with a transport block size varying between 0 and 25558 respectively.
Although the quality of HSDPA data communication between a NodeB and an UE with a BLER around 10% is satisfactory, there may be cases where the data rate received by the UE can not be processed. As an example, the Digital Signal Processing (DSP) resources existing in the UE might be required by other applications and for processing other tasks. Also, there might be a temporary lack of DSP resources in the UE . . . .
In such a situation, there is a clear need to allow the UE to take some kind of control on the data rate received from the NodeB, while avoiding too much disturbance of the NodeB.
Known HSDPA mechanisms do not provide such flexibility and the UE is generally not allowed to limit in any way the data rate in the downlink when necessary or simply appropriate.
In the non published french patent application no 09/51385 filed on 5. March 2009 and entitled “Procédé de contrôle du conctionnement d'une unite de traitement d'un appareil de communication sans fil, et appareil de communication corrrespondant>> filed on behalf of ST WIRELESS SA, there is described a first technique for providing such control on the downlink data rate, which technique is based on the saturation of the CQI being reported by the UE to the NodeB and corresponds to a maximum value which the UE is prepared to process.
However, it should be noticed that many NodeBs might not take into consideration the particular value of CQI being reported by the UE and simply proceed with their own computation of the CQI. In that case, as illustrated in FIG. 3, there would be no limitation in the data rate and the NodeB would keep the control on the downlink data rate based on its own calculation of the CQI.
In such a context, there is a strong desire to propose an alternative solution to improve, in some way, the control of the HSDPA downlink data rate that the UE may have or wish to have, without significantly disturbing the NodeB.